1. Field of the Invention
The present invention relates to a control and method for recording data on an overwritable optical recording medium. The control and method effectively replace previously recorded data, regardless of the location of the data on the recording medium.
2. Description of Related Art
In recent years, optical recording and retrieval methods have become well known. These optical recording and retrieval methods satisfy a variety of needs, such as: high density; large capacity; high access speed; and high recording; and retrieval speeds. Also, the recording devices, retrieval devices and recording media, which employ the above optical recording and retrieval methods, have become more well-known.
There are several known optical recording and retrieval methods. These include optical recording and retrieval methods that: 1) form holes in the recording medium using heat; 2) change phases; and 3) use magnetooptical principles. Phase change and magnetooptical methods can 1) replace data after data has been recorded; 2) record new data; and 3) repeat the process numerous times. These phase change and magnetooptical methods are widely used, for example, such as in external memories for computers and consumer audio equipment.
Until recently, it has been impossible to replace or "overwrite" previously recorded data with optical and retrieval methods. Overwriting consists of recording new information on a medium that has data already been recorded on without first replacing the data, i.e., the data is essentially replaced by overwriting. However, an optical recording method has been proposed where overwriting is achieved by modulating the intensity of a beam that irradiates a recording medium. The modulation is based on the digitized data that will be recorded. Further, overwritable optical recording media and recording devices, which are capable of overwriting using the above methods, are also known. For example, U.S. Pat. No. 5,239,524 (equivalents include Japanese Laid-Open Patent Publication Sho 62-175948 and DE 3,619,618A1) disclose this type of overwriting magnetooptical recording methods.
In U.S. Pat. No. 5,239,524, the contents of which are fully incorporated herein, an overwritable or magnetooptical recording medium is used in magnetooptical recording and retrieval. The magnetooptical medium comprises a plurality of magnetic layers, each layer having at least one perpendicularly arranged magnetic layer as the recording layer. The magnetic layer is comprised of any suitable material, such as, for example, amorphous TbFe, TbFeCo, GdFe, GdFeCo, DyFe, or DyFeCo, and the like.
The recording medium used in the magnetooptical recording of U.S. Pat. No. 5,239,524 is an overwritable multi-layer magnetooptical recording medium containing a memory layer or M layer that functions as a recording and retrieval layer, and a supplementary recording layer or W layer. The memory layer M comprises a vertically magnetizable magnetic film. The supplementary recording layer W also comprises a vertically magnetizable magnetic film. Therefore, the data, which is usually stored on both the supplementary recording layer W and the memory layer M, for example stored as bits, can be exchange-coupled, as explained in U.S. Pat. No. 5,239,524, if desired. During a room temperature exchange-couple process, the magnetic orientation of data on the memory layer M does not change, and the magnetization of the data on the supplementary recording layer W will be oriented in a preset orientation as the auxiliary recording layer W has a lower holding power force or coercivity Hc at room temperature, and a higher curie point Tc, than the memory layer M, as discussed in U.S. Pat. No. 5,239,524.
Further, data can be recorded on the memory layer M, and possibly also on the auxiliary recording layer WO. The recording of data on the separate layers is conducted by the data being magnetized in the vertical direction or "A" orientation, and data being magnetization in an opposite direction or "anti-A" orientation, as discussed in U.S. Pat. No. 5,239,524. The magnetooptical recording medium permits the magnetic orientation of the auxiliary recording layer W to be aligned in a single direction by a magnetic field means, for example such as an initializing auxiliary magnetic field, Hini. The magnetic orientation of the memory layer M is not reversed at this time. Furthermore, the magnetic orientation of the auxiliary recording layer W, which has been previously aligned in a single direction, is not reversed, even under the exchange-coupling force exerted by the memory layer M. The magnetic orientation of the memory layer M is not reversed, even under an exchange-coupling force exerted by the auxiliary recording layer W.
With the magnetooptical recording method as discussed in U.S. Pat. No. 5,239,524, only the magnetic orientation of the auxiliary recording layer W is aligned in a single direction by magnetic field means prior to recording data. Additionally, a laser beam, which has its pulse modulated based on digitized data, irradiates the recording medium, where the laser beam intensity is varied between a high level P.sub.H and a low level P.sub.L, as explained in U.S. Pat. No. 5,239,524. These levels correspond to a high and low level of the laser beam's pulse. The low level is higher than a retrieval level P.sub.R with which the medium is irradiated during a retrieval step.
As discussed in U.S. Pat. No. 5,239,524, the laser is turned on at an "extremely low level" to access a predetermined recording location on the medium, even when recording is not going to occur. This extremely low level is the same as or very close to the retrieval level P.sub.R. When a low level laser beam irradiates the recording medium at a temperature, the magnetic orientation of the auxiliary recording layer W does not change. The magnetic orientation of the memory layer M is affected to remove any magnetic barriers between the memory layer M and the auxiliary recording layer W. This is a low temperature process, and the temperature range at which this low temperature process occurs is a low temperature process temperature T.sub.L.
On the other hand, at a higher temperatures where a high level laser beam irradiates the recording medium, the magnetic orientation of the auxiliary recording layer W becomes aligned with the direction of the recording magnetic field. The magnetic orientation of the memory layer M is affected to remove any magnetic barriers between the memory layer M and the auxiliary recording layer W. This is called a high temperature process, and the temperature range at which this high temperature process occurs is called a high temperature process temperature T.sub.H.
After irradiation by the laser beam, the magnetic orientation of the auxiliary recording layer W, which had been aligned with the direction of the recording magnetic field by high level laser beam irradiation, is realigned with the magnetic orientation of the recording magnetic field. Accordingly, if the magnetic orientation of the magnetic field means and the magnetic orientation of the recording field are opposed, it is possible to repeatedly record or overwrite on the memory layer, even if data has been previously recorded. This is the principle of light modulation magnetooptical recording. In other words, the recorded data or bits are formed by high level laser beam irradiation, and the data or bits are replaced by low level laser beam irradiation. Thus, the new data replaces or "overwrites" of the old data.
To optimize the length and thickness of the mark of the signal pulse when recording on an optical recording medium, the optimum laser beam intensities should be set based on a temperature of the recording medium and a temperature of the environment. This process of finding the optimum laser beam intensities is called test recording. There are known magnetooptical disk recording apparatuses that conduct test recordings using different methods. On conventional optical recording media, which cannot be overwritten, i.e., non-overwrite media, test recording is conducted by causing the intensities to change, while keeping the ratio of the two values of laser beam intensities constant. Thus, the optimum laser beam intensities are can be determined.
However, with optical intensity modulation overwrite recording, a low level laser beam intensity P.sub.L is involved in both recording and overwrite recording. Accordingly in non-overwrite media, by only changing the intensities while keeping the ratio of the two laser beam intensities constant, the low level P.sub.L is set too low. Accordingly, poor replacing results during overwrite recording.